The present invention relates generally to systems and methods for generating electrical and/or pressure pulses, and more particularly, to such systems and methods that generate electrical and pressure pulses by utilizing thermal waves propagating along nanostructures, such as carbon nanotubes.
Portable energy storage and delivery is a key requirement of modern transportation systems and facilitates the proliferation of portable electronic devices. This rapidly growing field already represents a multi-billion dollar per year market across the globe. The miniaturization of electronic devices, network nodes for communications, and remote sensors is driven in part by the favorable scaling of energy requirements for many applications. That is, the reduced energy demand can offset the reduced energy storage capacity. Some critical applications, however, do not scale favorably with reductions in size. For example, radio frequency (RF) communication over a practical distance imposes a fixed power demand. In addition, development of the next generation of autonomous and mobile sensors, robots, and off-grid wireless networks, particularly devices at the micro- and nano-scale, is often hampered by the lack of high power density energy systems of similar size.
Conventional approaches for solving these problems have significant disadvantages. For example, harvesting ambient thermal, solar, or acoustic/mechanical energy is appealing because of the small sizes of such devices and their ability to work with otherwise wasted energy. However, the power generated tends to be too small for applications such as long-distance communication (where the coverage radius scales with the square root of power) or acceleration. Harvesters can collect energy slowly over time and subsequently discharge it rapidly, but this requires additional energy storage systems that impose limits on the systems and/or devices.
Batteries are one of the most familiar forms of energy storage for electricity, but electrochemical energy density is fundamentally limited compared to storing energy in the chemical bonds of fuels. For example, ethanol has a specific energy storage of 26.8 MJ/kg, whereas lithium-ion batteries can only store 0.720 MJ/kg, about 2.7% of the capacity of ethanol. Further, ethanol's energy density is about 20 times larger in volume terms (i.e., energy per unit volume). Batteries also rely on internal mass transport to develop charge and therefore require large electrode surface areas. This means that even small batteries are formed as thin films, which are not ideal for compact devices. Still further, batteries slowly lose their charge over years, making them less ideal for long-term energy storage. For example, batteries with a two-year half-life will lose 31% of their charge in one year. Supercapacitors can exhibit substantially higher power densities (in weight and volume terms), but at the expense of energy density. Moreover, supercapacitors cannot hold their charge as long as batteries.
Fuel cells and engines utilize the large energy density of chemical fuels, but are more complicated to fabricate at small scale. However, their power density has been limited so far. Accordingly, there is a need for improved systems, devices and methods for generating electrical energy, and particularly for generating electrical pulses having high peak powers for use in miniaturized devices.